Thanks to both Dl65 and Raptor.You are both correct and I suspected as much.
It is a CD only device.Although I have only had the PC about a month,it is actually about 3 years old.The previous owner ran a small business and therefore had no need for hi-spec stuff.He just confirmed to me in a phone call that ,to save money,he just had a CD only device installed.Ach well,next months pay slip is going to be used to purchase an internal DVD re-writer.